1. Field of the Invention
The present invention relates to a hermetic electric compressor for refrigerating or air-conditioning apparatuses such as refrigerators and air-conditioners.
2. Discussion of Background
A hermetic electric compressor has a structure shown in its partial diagrams, FIGS. 1(a) and (b), and in its diagram, FIG. 2. The sealed housing 1 encloses a motor unit 2 consisting of a stator and a rotor and a compressing unit 3 driven by the motor unit 2 and retains a refrigeration oil 4 on the bottom. The motor unit 2 consists of a stator fixed to the sealed housing 1 along the outer periphery and a rotor which is held to leave a certain clearance from the inner periphery of the stator and connected to the compressing unit 3 via a crankshaft 5, and one of the magnet wires 6 in the stator is connected to a sealing power supply terminal 7 on the sealed housing 1 for electric power supply.
As shown in FIG. 1, the stator comprises a tubular layered iron core 8 with several slots 9 axially cut on the inner wall, magnet wires 6 fitted in the slots 9, insulating films 10 interposed between the core 8 and the magnet wires 6 and between the magnet wires 6 and binding strings 11 bundling the magnet wires 6. Conventionally, the magnet wires 6 are impregnated with an impregnating varnish 12 (an insulating varnish) such as a solventless polyester resin varnish comprising styrene as a reactive diluent or an epoxy/phenol type or epoxy type solvent-based varnish.
However, because a lot of volatile components vaporize from conventional solventless varnishes or solvent-based varnishes during the treatment, improvements are necessary in the view of hygienic safety and as measures against the odor.
In addition, because these impregnating varnishes are used with a refrigerant system comprising a fluorocarbon (refrigerant)/a refrigeration oil, they have to have high resistance to the refrigerant system such as lasting mechanical strength and little extractability into the refrigerant system.
On the other hand, although conventionally used chlorofluorocarbons such as dichlorodifluoromethane (R-12) and hydrochlorofluorocarbons such as monochlorodifluoromethane (R-22) are being replaced by hydrofluorocarbons such as 1,1,1,2-tetrafluoroethane (R-134a) as alternative refrigerants containing no chlorine atoms in molecules under the Freon controls stemming from the destruction of the ozone layer, conventionally used refrigeration oils of the mineral oil type or the alkylbenzene type are not compatible with polar hydrofluorocarbons. Therefore, polar refrigeration oils of the polyalkylene glycol, ester and ether types, which are compatible with hydrofluorocarbons, are being used as alternative refrigeration oils.
The motor unit in the sealed housing is exposed to the mixture of a refrigerant and a refrigeration oil having a high temperature and a high pressure whenever the hermetic electric compressor is in operation. Because alternative refrigerants (hydrofluorocarbons) and alternative refrigeration oils (refrigeration oils of the polyalkylene glycol, ester and ether types) are highly polar as compared with conventional refrigerants and refrigeration oils, they degrade or dissolve organic materials constituting a stator of a conventional motor unit such as insulating films and binding strings and varnish materials for impregnating varnishes and can cause problems such as damage to parts in the circuit of a refrigerating or air-conditioning apparatus or to insulation.
In particular, because conventional varnish materials are composed of monomers with little polarity such as styrene, oligomers extracted from a cured varnish which are incompatible with alternative refrigeration oils precipitate in the refrigerant system comprising an alternative refrigerant/an alternative refrigeration oil and accumulate as sludge in narrows such as capillaries or an expansion valve in the refrigerating or air-conditioning cycle and cause troubles by clogging these narrows during long-time operation.
On the other hand, conventionally used solvent-based varnishes have a problem of a large energy loss during the curing step because they contain not less than 50 wt % of a solvent which irrelevant to the curing reaction as a diluent. In addition, poor working environments and air pollution due to released solvents are a big problem in more environmentally regulated these days.